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What Is An Ignition Interlock Device?

Ignition Interlock

A breath alcohol ignition interlock device is a sensor that prevents anyone who has been drinking alcohol from starting the vehicle in which it has been installed.

If you are convicted of driving under the influence of alcohol (DUI), you could be ordered by the courts or your state’s department of motor vehicles to rent and install an ignition interlock in your car for as long as a year.

This interlock requires you to take a breath alcohol concentration (BAC) test every time you need to start your vehicle.

If, when you blow into the tester, your BAC registers above your designated limit (usually between 0.00 and 0.025), the starter on your vehicle is shut down and you cannot start it up.

In addition, this device can be used for random state-mandated rolling tests while you’re driving.

Most state courts will allow ignition interlock devices to be used as a condition of probation or driver’s license reinstatement following a DUI conviction. In 2003, more than 80,000 interlocks were used in this manner throughout the country.

Am I Required to Use an Ignition Interlock Device After A DUI?

You may find that your state makes an ignition interlock a required part of your court-mandated sentence when you are convicted for DUI.

Or perhaps your state DMV will require use of an ignition interlock before allowing you to retain or regain your driving privileges.

States are often more likely to require an interlock after multiple DUI convictions, although sometimes they are required after your first DUI conviction.

This is more likely if your BAC was excessively high (at least 0.15 in some states), if you caused an injury while driving under the influence, or if you refused to take a breath alcohol test.

Often, drivers convicted of DUI will have their driving privileges restricted for a time.

It is not unusual for these restrictions to include mandatory use of an ignition interlock until such time when full driving privileges are reinstated.

It is even possible to use an ignition interlock voluntarily. Sometimes drivers who struggle with controlling their alcohol intake will install these interlock devices on their own to help them to avoid driving after drinking too heavily.

How Much Does An Ignition Interlock Device Cost?

Ignition interlocks are sold or rented by private companies authorized or licensed by the state.

Renting an ignition interlock device generally costs between $70 and $100 per month, plus tax, and installing one can cost as much as $100 to $200.

You are expected to pay these costs, along with any maintenance expenses, and fees for downloading the records the device stores.

You might also be required to return occasionally to the location where you rented the equipment to have these stored records downloaded and the device reset, in order to continue driving.

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Is It Possible To Fool An Ignition Interlock Device?


Ignition interlock manufacturers have designed the devices to make it nearly impossible to “cheat.”

The interlock is specially programmed to prevent your vehicle from starting if you refuse to perform the BAC test, try to use some kind of mechanical device-or a friend-to blow into the tester for you, or if you tamper with the device.

A mechanical substitute won’t work because interlock devices will require the driver to perform certain tasks during the test that a machine cannot perform, like sucking in air or making a humming noise. Trying to substitute a sober friend is pointless, because you’ll also be subjected to random tests while driving.

Refuse to take the random driving test, and your lights will flash and your horn will blare continuously until you pull over and test.

Tampering with an ignition interlock device is even worse, as it will completely shut down your ignition system. Your vehicle will not operate again unless you take the device back to the supplier, have the test results AND the evidence of your tampering downloaded, and turn it all over to the court or DMV. This will definitely not help your case.

Where Can I Get More Information about Ignition Interlock Devices?

Speak to a DUI attorney in your area, who can inform you about the likelihood that an ignition interlock device could be used in your case.

He or she can also explain how your local court system or state DMV tends to use ignition interlock devices.

Schedule a free consultation with a local DUI lawyer today, and learn what you need to know about these devices.